RT-Link: A Time-Synchronized Link Protocol Anthony Rowe, Rahul - - PowerPoint PPT Presentation

RT-Link:

A Time-Synchronized Link Protocol

Anthony Rowe, Rahul Mangharam, Raj Rajkumar C i M ll U i it Carnegie Mellon University

What is RT-Link?

• RT-Link is a scalable energy efficient

multi-hop link protocol for:

– Industrial Control S ill – Surveillance – Inventory Tracking

• Provides Bounded Latency, Energy

Efficient and Deterministic Operation Efficient and Deterministic Operation

– Achieved through global time synchronization

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NIOSH Research Coal Mine

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Overview

• Hardware Assisted Global Time Synchronization
• RT-Link TDMA Protocol
• Energy Benefits of TDMA

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CMU FireFly Sensor Node

Hardware Time Sync CC2420 Radio Atmega128L Processor FLASH Temperature Expansion Port Audio Light Acceleration Expansion Port 5 PIR Motion

Global Time Synchronization Beacon y

Power Grid AM Transmitter Antenna

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Carrier Current Adapter Nodes

FireFly v2.0 y

Expansion Port Chipcon cc2420 802.15.4 Radio Atmega 1281 8K RAM 128K ROM Programming Port Mini-SD slot 128K ROM (RDS, carrier current, atomic clock modules)

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FireFly Synchronization Hardware

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Current CSMA based approaches

• Low-Power Listen Carrier Sense Multiple Access

(LPL CSMA) h (LPL-CSMA) schemes

Radio RX Radio TX

Check for Data

Radio TX

Extended TX Preamble

• Tradeoff: Check Faster or Listen Longer

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LPL-CSMA

ms)

Multiple Sampling Intervals

k Interval (m

(yrs)

40 min 60 min

mal Check

Life (

20 min 30 min 40 min

Optim

Data Sampling Interval (min) Radio Check Interval (ms)

Radio Check Interval

Radio RX

10 Data Sampling Interval

Radio TX

TDMA-Based Approach (RT-Link)

Time-Sync Cycle AM Sync Pulse y y Frame (32 per TDMA Cycle) Scheduled Slots Contention Slots 32 Slots Per Frame

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RT-Link Graph Coloring

• Color Topology Graph to Avoid Collisions

Each Color represents a TDMA slot

• Each Color represents a TDMA slot

a

TX

a f

Gateway

a f a

RX TX

b c f e b c f e b

TX RX

d c

TX RX

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TDMA Frame

In-Band Time Synchronization y

a c

Gateway

a c f m b d e b d e

Header Packet Body

Time Slot Application Data

Header Packet Body

Overhearing Node Now Knows Time

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Starting Time of Overheard Packet Overhearing Node Now Knows Time Offset Within Cycle…

Lifetime Given Periodic Sampling

s) ifetime (yrs

Optimal

Li

Optimal LPL-CSMA RT-Link Hardware RT-Link Software

S l I t l ( i )

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Sample Interval (min)

Lifetime vs Neighboring Degree

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Logical Topology Pruning

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NIOSH Research Coal Mine

In-Band Time In-Band Time Synchronization Global Time Global Time Sync Pulse “Leaky Feeder”

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Conclusion

• Hardware-based Time Synchronization is a

b t d l bl ti robust and scalable option Global Time Synchronization is economical

• Global Time Synchronization is economical

and convenient for indoor and outdoor deployments p y

• RT-Link achieves practical lifetimes of 2 years

p y

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Questions?

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